Sealing plugs of the type referred to herein are employed to seal the engine oil fill pipe of an internal combustion engine, most commonly those used in trucks and heavy-duty equipment. The purpose of the sealing plug is to prevent the escape of oil and fumes from the fill pipe and to prevent foreign objects from entering the fill pipe. Since the sealing plug is used with an internal combustion engine, an important design consideration is that the sealing plug must not vibrate out of the fill pipe. Hence, most users specify a minimum withdrawal force to insure against the sealing plug vibrating loose. As a result, the design of current sealing plugs include relatively elaborate means for wedging the sealing plug in the fill pipe.
One of the most common sealing plugs currently employed includes an expandable generally cylindrical plug body and a device for mechanically expanding the plug body after it is located in the fill pipe. More specifically, the expandable plug body is usually located between a pair of plates which are joined in such a manner that they can be drawn together. This results in a lateral expansion of the plug body against the walls of the fill pipe. The plates are drawn together by means of a threaded member which joins the two plates so that rotation of the threaded member causes relative movement between the plates or a toggle device. Although such sealing plugs function adequately, the use of a threaded member or toggle device for expanding the plug body adds greatly to the manufacturing cost. Additionally, removing and replacing the sealing plug in the fill pipe is inconvenient due to the required manipulation of the device for expanding the plug body.
Another consideration which is becoming increasingly important is that the device for expanding the plug body requires a handle of some type which extends a significant distance out of the sealing plug thus presenting a safety hazard. Recent safety requirements have called for the elimination of such handles.